1. Field of the Invention
The invention involves catheters usable in medical evaluations of a condition of a living body, and more particularly, catheters that can detect based on electric, ultrasonic, or other types of sensing methods.
2. Description of Related Art
The related art can be reviewed via published patent applications, issued patents, and scholarly articles published in various medical and scientific journals. First, the following are the published applications and issued patents.
Published Patent Applications
The full disclosures of the following published patent applications are all incorporated herein by this reference:    20010021841 Title: “Automated longitudinal position translator for ultrasonic imaging probes, and methods of using same”
This discloses a longitudinal position translator that includes a probe drive module and a linear translation module. The probe drive module is coupled operatively to an ultrasonic imaging probe assembly having a distally located ultrasound transducer subassembly in such a manner that longitudinal shifting of the transducer subassembly may be effected.    20010021811 Title: “Method and apparatus for intravascular two-dimensional ultrasonography”
This discloses a catheter for insertion in the blood vessel of a patient for ultrasonically imaging the vessel wall. The catheter includes a tubular element and an internally housed drive cable for effective circumferential scan about the catheter of an ultrasonic generating means.    20010021805 Title: “Method and apparatus using shaped field of repositionable magnet to guide implant
This discloses methods and apparatuses for displaying and using a shaped field of a repositionable magnet to move, guide, and/or steer a magnetic seed or catheter in living tissue for medicinal purposes.    20010020149 Title: “Safety mechanism and methods to prevent rotating imaging device from exiting a catheter”
This discloses systems and methods to prevent rotation of an imaging device if the imaging device is advanced beyond a distal end of a catheter.    20010020126 Title: “Systems And Methods For Visualizing Tissue During Diagnostic Or Therapeutic Procedures”
This discloses a catheter tube that carries an imaging element for visualizing tissue. The catheter tube also carries a support structure, which extends beyond the imaging element for contacting surrounding tissue away from the imaging element. The support element stabilizes the imaging element, while the imaging element visualizes tissue in the interior body region. The support structure also carries a diagnostic or therapeutic component to contact surrounding tissue.    20010016687 Title: “Ultrasound imaging guidewire with static central core and tip”
This discloses an ultrasound imaging guidewire, that is inserted into a patient's body. The guidewire has a static central core and an imaging guidewire body comprising an acoustical scanning device. The acoustical scanning device can be rotated to obtain 360 degree acoustical images of a site of interest in the patient's body.    20010011889 Title: “Magnetic resonance imaging device”
This discloses an imaging probe having all components necessary to allow magnetic resonance measurements and imaging of local surroundings of the probe.    20010009976 Title: “Systems for recording use of structures deployed in association with heart tissue”
This discloses an image controller that generates an image of a structure while in use with heart tissue in a patient.    20010007940 Title: “Medical device having ultrasound imaging and therapeutic means”
This discloses an ultrasound transducer for ultrasound imaging, RF thermal therapy, cryogenic therapy and temperature sensing, for treating a tissue or lesion.
Issued Patents
The full disclosures of the following patents are all incorporated herein by this reference:    U.S. Pat. No. 6,283,920 Ultrasound transducer assembly    U.S. Pat. No. 6,277,077 Catheter including ultrasound transducer with emissions attenuation    U.S. Pat. No. 6,267,727 Methods and apparatus for non-uniform rotation distortion detection in an intravascular ultrasound imaging system    U.S. Pat. No. 6,266,564 Method and device for electronically controlling the beating of a heart    U.S. Pat. No. 6,263,229 Miniature magnetic resonance catheter coils and related methods    U.S. Pat. No. 6,251,078 Preamplifier and protection circuit for an ultrasound catheter    U.S. Pat. No. 6,246,899 Ultrasound locating system having ablation capabilities    U.S. Pat. No. 6,233,477 Catheter system having controllable ultrasound locating means    U.S. Pat. No. 6,216,026 Method of navigating a magnetic object, and MR device    U.S. Pat. No. 6,210,356 Ultrasound assembly for use with a catheter    U.S. Pat. No. 6,200,269 Forward-scanning ultrasound catheter probe    U.S. Pat. No. 6,192,144 MR method for the image-assisted monitoring of the displacement of an object, and MR device for carry out the method    U.S. Pat. No. 6,178,346 Infrared endoscopic imaging in a liquid with suspended particles: method and apparatus    U.S. Pat. No. 6,173,205 Electrophysiology catheter    U.S. Pat. No. 6,165,127 Acoustic imaging catheter and the like    U.S. Pat. No. 6,162,179 Loop imaging catheter    U.S. Pat. No. 6,152,878 Intravascular ultrasound enhanced image and signal processing    U.S. Pat. No. 6,149,598 Ultrasound endoscope    U.S. Pat. No. 6,149,596 Ultrasonic catheter apparatus and method    U.S. Pat. No. 6,240,307 Endocardial mapping system    U.S. Pat. No. 5,662,108 Electrophysiology mapping system    U.S. Pat. No. 5,713,946 Apparatus and method for intrabody mapping    U.S. Pat. No. 5,546,951 Method and apparatus for studying cardiac arrhythmias    U.S. Pat. No. 5,480,422 Apparatus for treating cardiac arrhythmias    U.S. Pat. No. 6,277,077 Catheter including ultrasound transducer with emissions attenuation    U.S. Pat. No. 6,216,027 System for electrode localization using ultrasound    U.S. Pat. No. 6,014,579 Endocardial mapping catheter with movable electrode    U.S. Pat. No. 6,443,894 Medical diagnostic ultrasound system and method for mapping surface data for three dimensional imaging
The following related art comes from scholarly articles published in various medical and scientific journals. The numbers in brackets refer to the reference numbers listed at the end of the specification.
Heart rhythm disorders (atrial and ventricular arrhythmias) result in significant morbidity and mortality. Atrial fibrillation is the most common cardiac arrhythmia: it affects more than two million Americans, is responsible for one-third of all strokes over the age of 65 years, and annually costs 9 billion dollars to manage [1]. Furthermore, about 300,000 Americans die of sudden cardiac death annually, primarily due to ventricular tachyarrhythmias (ventricular tachycardia and fibrillation) which result in intractable, extremely rapid heartbeats [2]. Unfortunately, current pharmacological therapy for managing cardiac arrhythmias is often ineffective and, at times, can cause arrhythmias [3,4], thereby shifting emphasis to nonpharmacological therapy (such as ablation, pacing, and defibrillation) [5–8]. Catheter ablation has been successful in managing many atrial and a few ventricular tachyarrhythmias [9]. However, due to limitations in present mapping techniques, brief, chaotic, or complex arrhythmias such as atrial fibrillation and ventricular tachycardia cannot be mapped adequately, resulting in unsuccessful elimination of the arrhythmia. In addition, localizing abnormal beats and delivering and quantifying the effects of therapy such as ablation are very time consuming. Selecting appropriate pharmacological therapies and advancing nonpharmacological methods to manage cardiac arrhythmias are contingent on developing mapping techniques that identify mechanisms of arrhythmias, localize their sites of origin with respect to underlying cardiac anatomy, and elucidate effects of therapy. Therefore, to successfully manage cardiac arrhythmias, electrical-anatomical imaging on a beat-by-beat basis, simultaneously, and at multiple sites is required.
Electrical mapping of the heartbeat, whereby multielectrode arrays are placed on the exterior surface of the heart (epicardium) to directly record the electrical activity, has been applied extensively in both animals and humans [10–13]. Although epicardial mapping provides detailed information on sites of origin and mechanisms of abnormal heart rhythms (arrhythmias), its clinical application has great limitation: it is performed at the expense of open-chest surgery. In addition, epicardial mapping does not provide access to interior heart structures that play critical roles in the initiation and maintenance of abnormal heartbeats.
Many heart rhythm abnormalities (arrhythmias) originate from interior heart tissues (endocardium). Further, because the endocardium is more safely accessible (without surgery) than the epicardium, most electrical mapping techniques and delivery of nonpharmacological therapies (e.g. pacing and catheter ablation) have focused on endocardial approaches. However, current endocardial mapping techniques have certain limitations. Traditional electrode-catheter mapping performed during electrophysiology procedures is confined to a limited number of recording sites, is time consuming, and is carried out over several heartbeats without accounting for possible beat-to-beat variability in activation [14]. While newly introduced catheter-mapping approaches provide important three-dimensional positions of a roving electrode-catheter through the use of “special” sensors, mapping is still performed over several heartbeats [15–17]. On the other hand, although multielectrode basket-catheters [18,19] measure endocardial electrical activities at multiple sites simultaneously by expanding the basket inside the heart so that the electrodes are in direct contact with the endocardium, the basket is limited to a fixed number of recording sites, may not be in contact with the entire endocardium, and may result in irritation of the myocardium.
An alternative mapping approach utilizes a noncontact, multielectrode cavitary probe [20] that measures electrical activities (electrograms) from inside the blood-filled heart cavity from multiple directions simultaneously. The probe electrodes are not necessarily in direct contact with the endocardium; consequently, noncontact sensing results in a smoothed electrical potential pattern [21]. Cavitary probe mapping was also conducted on experimental myocardial infarction [22]. More recently, nonsurgical insertion of a noncontact, multielectrode balloon-catheter, that does not occlude the blood-filled cavity, has been reported in humans [23]. This catheter was used to compute electrograms on an ellipsoid that approximated the endocardium.
Present mapping systems cannot provide true images of endocardial anatomy. Present systems often delineate anatomical features based on (1) extensive use of fluoroscopy; (2) deployment of multiple catheters, or roving the catheters, at multiple locations; and (3) assumptions about properties of recorded electrograms in relation to underlying anatomy (e.g. electrograms facing a valve are low in amplitude). However, direct correlation between endocardial activation and cardiac anatomy is important in order to clearly identify the anatomical sources of abnormal heartbeats, to understand the mechanisms of cardiac arrhythmias and their sequences of activation within or around complex anatomical structures, and to deliver appropriate therapy.
Early applications of the “inverse problem” of electrocardiography sought to noninvasively reconstruct (compute) epicardial surface potentials (electrograms) and activation sequences of the heartbeat based on noncontact potentials measured at multiple sites on the body surface [24,25]. The computed epicardial potentials were in turn used to delineate information on cardiac sources within the underlying myocardium [26,27]. To solve the “inverse problem”, numeric techniques have been repeatedly tested on computer, animal, and human models [28–38]. Similarly, computing endocardial surface electrical potentials (electrograms) based on noncontact potentials (electrograms) measured with the use of a multielectrode cavitary probe constitutes a form of endocardial electrocardiographic “inverse problem.”
The objective of the endocardial electrocardiographic “inverse problem” is to compute virtual endocardial surface electrograms based on noncontact cavitary electrograms measured by multielectrode probes. Preliminary studies have demonstrated that methods for acquisition of cavitary electrograms and computation of endocardial electrograms in the beating heart have been established and their accuracy globally confirmed [39–50]. Determining the probe-endocardium geometrical relationship (i.e. probe position and orientation with respect to the endocardial surface) is required to solve the “inverse problem” and a prerequisite for accurate noncontact electrical-anatomical imaging. In initial studies, fluoroscopic imaging provided a means for beat-by-beat global validation of computed endocardial activation in the intact, beating heart [46–50]. Furthermore, epicardial echocardiography [45] was used to determine the probe-cavity geometrical model. However, complex geometry, such as that of the atrium, may not be easily characterized by transthoracic or epicardial echocardiography.
Accurate three-dimensional positioning of electrode-catheters at abnormal electrogram or ablation sites on the endocardium and repositioning of the catheters at specific sites are important for the success of ablation. The disadvantages of routine fluoroscopy during catheterization include radiation effects and limited three-dimensional localization of the catheter. New catheter-systems achieve better three-dimensional positioning by (1) using a specialized magnetic sensor at the tip of the catheter that determines its location with respect to an externally applied magnetic field [15], (2) calculating the distances between a roving intracardiac catheter and a reference catheter, each carrying multiple ultrasonic transducers [16], (3) measuring the field strength at the catheter tip-electrode, while applying three orthogonal currents through the patient's body to locate the catheter [17]; and (4) emitting a low-current locator signal from the catheter tip and determining its distance from a multielectrode cavitary probe [51]. With these mapping techniques true three-dimensional imaging of important endocardial anatomical structures is not readily integrated (only semi-realistic geometric approximations of the endocardial surface), and assumptions must often be made about properties of recorded electrograms in relation to underlying anatomy (e.g. electrograms facing the tricuspid and mitral annuli are low in amplitude).